The present invention relates to the technical field concerning automatic machines for forming packs of rolls, e.g. toilet paper rolls, tissue paper rolls, etc., arranged in groups or rows of one or more layers, by wrapping each pack with a protective wrapping sheet, e.g. polythene.
More precisely, the present invention relates to an elevator device mounted on machines for forming the packs of rolls, in the working station for initial wrapping step of the packs.
Automatic machines for forming packs of rolls, e.g. toilet paper rolls, tissue paper rolls, etc., include a working station for the initial wrapping step of the packs of rolls being formed.
The initial wrapping station, where a provisional wrapping is firstly applied to the pack of rolls, is situated between a substantially horizontal line for feeding the rolls to be arranged in groups to be packaged, and a substantially horizontal line conveying the packs being prepared away, situated above the rolls feeding line.
The working station for initial wrapping of the packs of rolls is aimed at partially wrapping the upper side of the packs with a protective sheet, and at transferring the pack with the protective sheet from the feeding line to the conveying line. The above working station includes substantially an elevator device equipped with an elevating plate, which reciprocates vertically from a lower end position, situated at the level of the rolls feeding line, and an upper end position, defined by positioning of the partially wrapped packs at a level just beneath a constraining plate, or a plurality of bars, of the conveying line.
While dwelling at the lower end position, the elevating plate of the above mentioned elevator device receives a pack of rolls to be packaged from the rolls feeding line and then raises the pack of rolls until it hits the protective sheet, kept stretched by appropriate means.
Consequently, the elevator device moves the rolls partially wrapped by the sheet into a guiding channel, where the rolls are conveyed, until the group passes through the aperture of means for folding the protective sheet, which are in open configuration and situated at the outlet of the conveying channel.
After having reached the upper end position, the elevator device places the rolls and the sheet against the constraining plate and within holding arms of the conveying line.
Then, the elevator device lowers the plate to the lower end position, to receive another pack of rolls to be packaged, while the folding means, moved to the closed configuration, fold the wrapping sheet under the pack of rolls.
Then, the conveying line carries the open-ended wrapped pack of rolls to the working stations for completion of the wrapping and sealing of the pack.
At present, in order to increase the production rate by increasing the number of packs obtained in the same time interval, the elevator device has been operated with always higher operation speed.
This results in considerable functional problems and disadvantages, because the high speed during the raising of the pack of rolls to be packaged makes the pack detach from the plate and bounce against the constraining plate of the conveying line, situated above, before the plate reaches its upper end position.
Thus, during the critical step of initial wrapping the pack of rolls, the rolls bounce continuously between the plate and the constraining plate of the conveying line.
As a result, the wrapping of the pack of rolls to be packaged becomes ruffled, because the rolls bounce continuously and detach from the sheet, and consequently they do not maintain the best configuration.
Consequently, the protective sheet is no longer smoothly applied and does not adhere perfectly to the pack of rolls being packaged and the rolls will be loosely packed.
In order to avoid this disadvantage, the operating speed of the elevator device has been controlled accurately.
In particular, the speed of the plate has been increased gradually, during the first part of the stroke, so as to prevent the packs of rolls from detaching.
However, due to obvious mechanical-kinetic reasons, the speed must be gradually reduced during the final portion of the stroke to avoid too rapid damages to the mechanism caused by stops, which are too sudden with respect to the inertial masses involved.
Obviously, the speed control must be performed while maintaining at the same time a high production rate, and it should possibly increase the latter.
Attempts made in the prior art until now, have not been capable of performing an effective control of the rolls with operation speed higher than the speed actually obtained, because of constructive and dynamic difficulties, ensuring at the same time high and optimal production rates.
According to another attempt to avoid the movements of the group of rolls on the plate, the rolls were kept as much compressed as possible during the raising step.
This was aimed at creating a kind of friction on the walls of the pack of rolls contrary to the motion of the pack raising, e.g. by reducing the transversal dimension of the guiding channel.
However, the above contrary action reduces the risk of bouncing movements between the pack of rolls and the plate, but on the other side, it can cause some imperfections in the wrapping of the pack with the protective sheet.
Actually, the arrangement of the rolls in the packages obtained by the above method is often imperfect and consequently, the look of the packages is not attractive for the consumer.
The object of the present invention is to propose an elevator device in machines for forming packs of rolls, which avoids the above mentioned disadvantages.
More precisely, the main object of the present invention is to propose an elevator device, which avoids undesired bounces of the pack of rolls during its raising toward the conveying line and partial wrapping in a protective sheet.
Another object of the present invention is to propose an elevator device, which allows to maintain high production rate of the machine for forming packs of rolls and, at the same time, ensures high packaging quality.
The above mentioned objects are obtained, in accordance with the contents of the claims, by means of an elevator device in a machine for forming packs of rolls, the machine including:
a feeding line for feeding rolls;
a conveying line situated above said feeding line for carrying away packs of rolls already formed;
upper constraining means disposed along the conveying line;
holding means of said conveying line, for holding a group of rolls being packed; and
an elevator device for taking the rolls from said feeding line to said conveying line, said elevator device including:
an elevation plate made to reciprocate vertically between a lower end position, situated at the level of said feeding line for receiving rolls from said feeding line thus forming a group of rolls on said elevation plate, and an upper end position, defined by positioning a group of rolls on said elevation plate at a level right below said constraining means;
a conveying channel for said group of rolls on said elevation plate, said conveying channel leading from said lower end position of said elevation plate up to said upper end position;
means for keeping a wrapping sheet spread crosswise at an intermediate point of said conveying channel, said wrapping sheet partially wrapping said group of rolls on said elevation plate;
an aperture made at top of said conveying channel;
folding means disposed right above said aperture for folding said wrapping sheet under said group of rolls on said elevation plate when said elevation plate is in said upper end position;
an auxiliary plate member, situated above said folding means and below said constraining means, said auxiliary plate member moving vertically between a position near and above said aperture, and a position in alignment with said constraining means of said conveying line, in step relation with operation of said elevation plate, for keeping said group of rolls on said elevation plate firm while said group of rolls is passing through said aperture to be placed within said holding means.